1. Technical Field
The present invention relates to a polarization element.
2. Related Art
As light modulation devices of various types of electro-optic devices, there are used liquid crystal devices. As a structure of the liquid crystal device, there is widely known a structure in which the liquid crystal layer is sandwiched between a pair of substrates disposed so as to be opposed to each other, and a polarization element for inputting the light with predetermined polarization into the liquid crystal layer and an oriented film for controlling the arrangement of the liquid crystal molecules when no voltage is applied thereto are typically provided.
As the polarization element, there are known a film type polarization element manufactured by stretching a resin film including iodine or dichroic dye in one direction thereby orienting the iodine or the dichroic dye in the stretching direction, and a wire-grid type polarization element formed by paving the surface of a transparent substrate with nano-scale thin lines.
The wire-grid type polarization element is made of an inorganic material, and therefore, has an advantage of being superior in heat resistance, and is preferably used in a place where heat resistance is particularly required. For example, it is preferably used as a polarization element for a light valve of a liquid crystal projector. As such a wire-grid polarization element as described above, there is disclosed a technology described in JP-A-2007-148344 (Document 1), for example.
In the Document 1, a metallic material is deposited using an oblique sputtering method executed in a tilted direction on concavo-convex portions formed on the substrate, and the metal microparticulate layer thus deposited is used as the thin lines, instead of using the related art method of forming the thin lines by patterning the metal film by etching. According to the Document 1, the method can provide the polarization element having a desired polarization property in the visible light range, and high productivity.
However, in the polarization element of the related art described above, there arises a problem that when the thin lines are formed at the convex portions on the substrate by executing the oblique sputtering, unevenness is caused in the amount of deposition of the inorganic microparticles as a material of the thin lines depending on the position in the surface of the substrate. In other words, in the method described in the Document 1, the distance from the material source of the metallic material varies in accordance with the position on the surface of the substrate. Therefore, there arises unevenness of about ±50% of the target size in each of the metallic materials deposited thereon depending on the position on the surface of the substrate. If the unevenness is caused in the size of the metallic material, the parameters closely related to the optical solid state properties of the polarization element, such as the distance between the adjacent thin lines, or the width or the height of the thin line vary, and therefore, it is not achievable to express the uniform optical solid state properties throughout the entire polarization element.